1. Environmental Thermal Engineering
Lecture # 13
Min soo Kim
Mechanical & Aerospace Engineering

2. Space Heating load

3. The types of heat loads ㅊ 20℃ 5℃ Through the sealing
Through the window
Through the wall
Through the sealing
Through the
shared wall
Through the floor

4. The kinds of heat loads The kinds of heat loads
① conducted heat by the temperature
difference
- through the window
- through the wall, roof
- through the shared wall
② leaking air
- by infiltration
③ entering air
- by ventilation
Entering air
Conducted heat by temperature difference
humidification
Leaking
air

5. Categories of heating and cooling loads
exfiltration
infiltration
Transmission
internal
Solar
Categories of heating and cooling loads

6. Design Criteria External condition Building structure / Insulation
Degree of
exposure /
Airtightness
Area of
window
Hours of use /
Occupied room
characteristic
Temperature
drop condition
Daily
temperature
range /
Lowest
Auxiliary
heating
system
Economic
feasibility

7. Internal condition Purpose of building Occupied room characteristic
Legal validity

8. Calculating heating loads
Heat Loss by
Conduction
Heat
loads
Setting up
external
design
criteria
Determine
internal
temperature
Calculating
overall
heat transfer
coefficient
Calculating
areas of
control
spaces
Leaking
Air Σ
Load
due to
Entering
Air

9. 1. Heat loss through external wall, roof, floor, and window
q : Heat loss through external wall, roof, floor, and window [W]
A : Area of wall, roof, floor, and window [㎡ ]
U : Overall coefficient of heat transfer [W/㎡ K]
: Indoor air temperature [K]
: Outdoor air temperature [K]

10. - Heat loss through underground wall
2. Heat loss through underground wall and floor
- Heat loss through underground wall
- Heat loss through underground floor
- Heat loss through floor on the surface of the earth

11. 2-1 Path of heat loss through underground (without insulator)
Heat flux
Radial isothermal line

12. 2-2 Path of heat loss through underground (with partial insulator)
Air temperature +1 +2 +3 +4 +5 +6 +7 +8 +9
+10
+11
+12
Indoor temperature

13. Heat loss coefficient, W/( K) Minimum width of the building, m 6 7.3
2-3 Heat loss through underground floor
Underground wall height
Heat loss coefficient, W/( K)
Minimum width of the building, m 6
7.3
8.5
9.7
1.5
0.18
0.16
0.15
0.13
1,8
0.17
0.14
0.12
2.1

14. 1) Sensible heat loss 3. Heat loss due to outdoor air infiltration
mo : Mass flow rate of outdoor air
cp : Specific heat of air
Q : Volume flow rate of outdoor air
vo : Specific volume

15. 2) Latent heat loss
- Humidification load to maintain optimum humidity level
ql : Required heat to increase humidity
from Wo to Wi [W]
Q : Volume flow rate of outdoor air infiltration [L/s]
Wi : Absolute humidity of indoor air
Wo : Absolute humidity of outdoor air
hfg : Latent heat of vapor

16. - Empirical prediction of air change rate
4. Outdoor air infiltration prediction
1) Method of air change
- Empirical prediction of air change rate
- ACH (Air Change per Hour) range : 0.5 ~ 2.0 (fresh outdoor air)
ex) Modern office building ACH
Outdoor air requirements per person = 36 CMH/person (ASHRAE)

17. - Prediction using pressure difference between indoor & outdoor
2) Cracking method
- Prediction using pressure difference between indoor & outdoor
and characteristics of window, wall, and door
Q : Volume flow rate of outdoor air infiltration
A : Valid leaking area of the crack
C : Flow factor depending on crack shape and flow characteristics
ΔP: Pressure difference between indoor & outdoor
n : Flow characteristic factor at the crack
(0.4 ~ 1.0)

18. Outdoor air characteristic at door and window

19. Window category Wood Double-hung (Locked) Other types
Tight-fitting window
K = 1.0
Weatherstripped average gap
(1/64”. Crack)
Wood casement and awning windows; weatherstripped
Metal casement windows;
weatherstripped
Average-fitting window
K = 2.0
Non-
weatherstripped average gap (1/64”. Crack)
All types of vertical and horizontal sliding windows; weatherstripped. Note: If average gap (1/64”. Crack) this could be tight-fitting window
Weatherstripped large gap (3/32”. Crack)
Nonweatherstripped. Note:
If large gap (3/32”. Crack)
this cuold be a loose-fitting window
Loose-fitting window
K = 6.0
weatherstripped large gap (3/32”. Crack)
Vertical and horizontal sliding windows; nonweatherstripped
Reference : ASHRAE Cooling and Heating Load Calculation Manual, 2nd ed., 1992.

20. Door category Tight-fitting door K = 1.0
Very small perimeter gap and perfect fit weatherstripping - often characteristic of new doors
Average-fitting door
K = 2.0
Small perimeter gap having stop trim fitting properly around door and weatherstripped
Loose-fitting door
K = 6.0
Larger perimeter gap having poor fitting stop trim and weatherstripped or
Small perimeter gap with no weatherstripping
Reference : ASHRAE Cooling and Heating Load Calculation Manual, 2nd ed., 1992.

21. : Pressure difference due to wind ----- (a)
: Pressure difference due to chimney effects (b)
: Pressure difference due to pressurizations (c)
* Pressure differences are positive values
when they make air flow into the building

22. (a) Pressure difference due to wind
(pressure difference when Vf =0)
Vw : Speed of wind
Vf : Final speed of wind at the border of the building
Cp : Pressure coefficient

23. - Pressure coefficient ( )
Depend on direction and shape of the building
* Average pressure coefficient of low-rise building

24. Average pressure coefficient of high-rise building
Reference : ASHRAE Handbook, Fundamentals Volume, 1989

25. Theoretical pressure difference without internal barriers
(b) Pressure difference due to chimney effects
- Chimney effects : Occurs when indoor & outdoor air densities
are different
- Neutral pressure height : Height where pressure difference is
zero when only chimney effect is considered
Theoretical pressure difference without internal barriers
Po : Outdoor pressure [Pa]
h : Vertical distance from neutral pressure height [m]
To : Outdoor temperature [K]
Ti : Indoor temperature [K]
Ra : Gas constant of air

26. Pressure difference due to chimney effects
* Ventilation coefficient
Pressure difference due to chimney effects
Po : Outdoor pressure [Pa]
h : Vertical distance from neutral pressure height [m]
To : Outdoor temperature [K]
Ti : Indoor temperature [K]
Ra : Gas constant of air

27. * Pressure difference due to chimney effects
Reference : ASHRAE GRP 158, Cooling and heating Load Calculation Manual, 2nd ed., 1992

28. 5. Heat loss through the duct system
U : Overall heat transfer coefficient
: Exterior surface area of duct
: Mean temperature difference between air inside duct and
surrounding

29. = The outside temperature – Air temperature inside the duct
Example
⊙ Calculate the heat loss for circular duct when air flows 1000 cfm at 120 F. The length and diameter of duct are 25 ft and 16 in respectively. The insulator of duct is 1 in fiber glass and overall heat transfer coefficient is 0.2 Btu/(hr- -F). The outside temperature is 12F.
Sol)
= The outside temperature – Air temperature inside the duct
: Surface area of duct( )

30. Bin method
⊙ Method to calculatee heating load with the outdoor temperature changes within a certain period, energy consumption of building depends on outdoor temperature, and occurrence (hours)
Heating load
Heating load to maintain proper indoor temperature
(Q)
Outdoor temperature
(to)
Balance point : (tb)
Point which heating & cooling are not required

31. ⊙ It is required to consider a case that people are inside the building (occupied) to compute heating load of the building.
Heating load d
Occupied
Unoccupied
Internal load
Outdoor temperature

32. ⊙ Partial Load Factor (PLF)
※ : Performance degradation coefficient

33. ⊙ Occupied run time (Hr)
⊙ Unoccupied run time (Hr)

34. ⊙ Occupied Electrical resistance Input (kW)
⊙ Unoccupied Electrical resistance Input (kW)
⊙ Total Energy (kWh)

35. ⊙ Sequence of Bin method
Set building load using load curve
Set unit capacity
Calculate theoretical operating time as ratio of building load and unit capacity
Calculate partial load ratio
Calculate real operating time ratio
Calculate real operating time (Bin hour * Real operating time ratio)
Calculate power consumption of unit
Calculate energy required (Power consumption of unit * Real operating time)
Set the cost of unit energy
Calculate energy cost of a single bin (Cost of unit energy * Energy required )
Repeat 1~10 for all the other bins

36. # Example
⊙ Consider a building in the state of Oklahoma. The curve of system load is expressed as follow.
Load curve of residential hours (Group A) = 267,000 – 4860×to [kW]
Load curve of nonresidential hours (Group B) = 316,000 – 4860×to [kW]
Use performance curve of heat pump, and assume degradation factor is All bins in table is happened in cold whether. Calculate necessary energy of heating building to keep 70 F for residential and nonresidential group.
♣ Appendix 1 : transfer of bin hours of group A and B.
♣ Appendix 2 : Ratio of bin hours at each times
♣ Appendix 3 : Bin hours for in the state of Oklahoma yearly
♣ Appendix 4 : Calculate bin hours for groups at each hours
♣ Appendix 5 : Operation curve of heat pump
♣ Appendix 6 : Heating capacity of heat pump at 6000 CFM
♣ Appendix 7 : Solution

37. ♣ Appendix 1

38. Table. Bin hour ratio of time shifts
♣ Appendix 2
Table. Bin hour ratio of time shifts
Time Group
Hours in Shift A in Each Group
Days in Shift A in Each Group
Total Occupied Hours in Each Group
Total Hours in Each Group
Shift A Fraction in Each Group
Shift B Fraction in Each Group I 28
0.0
1.0 II 1 5
0.18
0.82
III 4 20
0.71
0.29 IV V 2 10
0.36
0.64 VI

39. Table. Annual bin hour of Oclahoma
♣ Appendix 3
Table. Annual bin hour of Oclahoma
Bin Temperature (F)
Shift A Hours Each Time Group
Total Hours
1-4 I
5-8 II
9-12
III
13-16 IV
17-20 V
21-24 VI
102 2 97 5 70 29
104 92 55
153 88
296 87
116
145
120 24
407 82 20 33
148
168 96
618 77
121 93
132
115
144
171
776 72
229
221
138
118
117
186
1009 67
161 98
136
747 62 99 95
135
642 57
105
108 81
601 52
103
137 94
133
684 47
100 66
122
569 42
150 91
140
667 37 89 54 76
621 32
107 74 40 50
504 27 63 51 22 36 41 23 17 31 19 1 16 12 7 3 18

40. Table. Bin hours of time shifts
♣ Appendix 4
Table. Bin hours of time shifts
Bin Temperature
(F)
Shift A Hours Each Time Group
I (0.00”)
II (0.18”)
III (0.71”)
IV (0.71”)
V (0.36”)
VI (0.00”)
102 1 97 4 50 10 92 39
109 32 87 82
103 43 6
105 60 77 17 94 52 72 40 98 84 42 67 29 70 33 62 18 96 35 57 19 75 48 47 71 31 22 37 28 63 38 27 25 53 9 7 16 12 8 2

41. Characteristics of heat pump
♣ Appendix 5
Characteristics of heat pump

42. Table. Heating capacity of heat pump where air flow rate is 6000 CFM
♣ Appendix 6
Table. Heating capacity of heat pump where air flow rate is 6000 CFM
Outdoor temperature
(F)
Heating Capacity, Btu/hr x 1000 at
Indoor Dry Bulb Temperature (F)
Total Power Input (kW) at Indoor Dry Bulb Temperature (F) 60 70 75 80 -3
70.5
68.8
68.0
67.2
12.9
13.3
13.5
13.7 2
78.7
76.9
75.9
75.0
13.4
13.8
14.0
14.2 7
87.0
84.9
83.9
82.9
14.5
14.7 12
95.2
93.0
91.8
90.7
14.3
14.9
15.2 17
103.0
101.0
99.8
98.6
15.4
15.7 22
111.0
109.0
108.0
106.0
15.0
15.5
16.0 27
120.0
117.0
115.0
114.0
15.3
15.8
16.3 32
128.0
125.0
123.0
121.0
16.6 37
140.0
136.0
135.0
133.0
16.8
17.1 42
158.0
154.0
152.0
150.0
16.9
17.4
17.7
18.0 47
176.0
172.0
170.0
168.0
18.3
18.6
18.9 52
188.0
184.0
182.0
179.0
18.2
19.1
19.4 57
201.0
196.0
193.0
191.0
18.7
19.3
19.7
20.0 62
213.0
208.0
205.0
202.0
19.2
19.9
20.2
20.5 67
225.0
219.0
217.0
214.0
20.4
20.7
21.0
* Correction factor – Value with different air flow rate – (Value with 6000 CFM air flow x Correction factor)

43. Solution
♣ Appendix 1

44. Table. Bin hour ratio of time shifts
♣ Appendix 2
Table. Bin hour ratio of time shifts
Time Group
Hours in Shift A in Each Group
Days in Shift A in Each Group
Total Occupied Hours in Each Group
Total Hours in Each Group
Shift A Fraction in Each Group
Shift B Fraction in Each Group I 28
0.0
1.0 II 1 5
0.18
0.82
III 4 20
0.71
0.29 IV V 2 10
0.36
0.64 VI
X axis value of appendix 1
1-shift A fraction in Each Group
Y axis value of appendix 2
Total hours in each group
Total Occupied Hours in Each Group
Total Hours in Each Group

45. Table. Annual bin hour of Oclahoma
♣ Appendix 3
Table. Annual bin hour of Oclahoma
Bin Temperature (F)
Shift A Hours Each Time Group
Total Hours
1-4 I
5-8 II
9-12
III
13-16 IV
17-20 V
21-24 VI
102 2 97 5 70 29
104 92 55
153 88
296 87
116
145
120 24
407 82 20 33
148
168 96
618 77
121 93
132
115
144
171
776 72
229
221
138
118
117
186
1009 67
161 98
136
747 62 99 95
135
642 57
105
108 81
601 52
103
137 94
133
684 47
100 66
122
569 42
150 91
140
667 37 89 54 76
621 32
107 74 40 50
504 27 63 51 22 36 41 23 17 31 19 1 16 12 7 3 18

46. Table. Computing bin hours for each time group
♣ Appendix 4
Total hours
– Shift A hours
Table. Computing bin hours for each time group
Bin Temperature
(F)
Shift A Hours Each Time Group
Shift A Hours
Shift B Hours
I (0.00”)
II (0.18”)
III (0.71”)
IV (0.71”)
V (0.36”)
VI (0.00”)
102 1 97 4 50 10 64 40 92 39
109 32
179
117 87 82
103 43
229
178 6
105 60
280
338 77 17 94 52
244
532 72 98 84 42
264
745 67 29 70 33
202
545 62 18 96 35
216
426 57 19 75
212
389 48
230
454 47 71 31
166
403 22
172
495 37 28 63 38 27
156
465 25 53
124
380 9 54
175 7 16 12 8 44
127 2 21 74 3 15
Total
2861
5899
“ Ratio of occupied time shift (shift A)

47. ♣ Appendix 6
Table. Heating capacity of heat pump where air flow rate is 6000 CFM
Outdoor temperature
(F)
Heating Capacity, Btu/hr x 1000 at
Indoor Dry Bulb Temperature (F)
Total Power Input (kW) at Indoor Dry Bulb Temperature (F) 60 70 75 80 -3
70.5
68.8
68.0
67.2
12.9
13.3
13.5
13.7 2
78.7
76.9
75.9
75.0
13.4
13.8
14.0
14.2 7
87.0
84.9
83.9
82.9
14.5
14.7 12
95.2
93.0
91.8
90.7
14.3
14.9
15.2 17
103.0
101.0
99.8
98.6
15.4
15.7 22
111.0
109.0
108.0
106.0
15.0
15.5
16.0 27
120.0
117.0
115.0
114.0
15.3
15.8
16.3 32
128.0
125.0
123.0
121.0
16.6 37
140.0
136.0
135.0
133.0
16.8
17.1 42
158.0
154.0
152.0
150.0
16.9
17.4
17.7
18.0 47
176.0
172.0
170.0
168.0
18.3
18.6
18.9 52
188.0
184.0
182.0
179.0
18.2
19.1
19.4 57
201.0
196.0
193.0
191.0
18.7
19.3
19.7
20.0 62
213.0
208.0
205.0
202.0
19.2
19.9
20.2
20.5 67
225.0
219.0
217.0
214.0
20.4
20.7
21.0
* Correction factor – Value with different air flow rate – (Value with 6000 CFM air flow x Correction factor)
Linear interpolation
Linear interpolation
 C = 2367to + 60,767
 P = 0.103to

48. Characteristics of heat pump
♣ Appendix 5
Characteristics of heat pump

49. Power consumption can be calculated as below by same way.
♣ Appendix 7
Given load curve is suitable for applying bin method. For each shifts, it is possible to calculate balance point by set and zero.
Occupied case
 to=267,000/4860 = 55 F
Unoccupied case
 tuo=316,000/4860 = 65 F
Therefore, we don’t need to consider temperature bins higher than 65 F.
Steady state performance of heat pump can be computed as below with appendix 6. Choose two heating capacity and temperature (17 F, Btu/hr and 47 F, Btu/hr) and suppose heating capacity is linearly dependent to outdoor temperature(aX+b=Y). The result is shown below.
 C = 2367to + 60,767 Btu/hr
Power consumption can be calculated as below by same way.
 P = 0.103to kW

50. Equipment Capacity (J/K)
# Calculate sequence of example prob. (1-1)
Bin Temperature
Occupied Hours
Unoccupied Hours
Occupied Load
(Btu/hr)
Unoccupied Load (kW)
Equipment Capacity (J/K)
Occupied PLF 1
Table 5-6 2 3 4
Given Eq. 5-26 5
Given Eq. 5-27 6
Given Eq. 5-28 7
Eq. 5-24, Dc=0.25 62
216
426
14,680
207,521
0.75 57
212
389
38,980
195,686 52
230
454
14,280
63,280
183,851
0.77 47
166
403
38,580
87,580
172,016
0.81 42
172
495
62,880
111,880
160,181
0.85 37
156
465
87,180
136,180
148,346
0.90 32
124
380
111,480
160,480
136,511
0.95 27 54
175
135,780
184,780
124,676
1.00 22
127
160,080
209,080
112,841 17 21 74
184,380
233,380
101,006 12 15
208,680
257,680
89,171
From appendix 4
From load curve
From interpolation

51. # Calculate sequence of example prob. (1-2)
Unoccupied PLF
Occupied Run Time (Hr)
Unoccupied Run Time (Hr)
Power Input (kW)
Occupied Electrical resistance Input (kW)
Unoccupied Electrical resistance Input (kW)
Total Energy (kWh) 8
Eq. 5-24
Dc = 0.29 9
4x2/(6x7) 10
5x3/(6x8) 11
Given
Eq. 5-29 12
4-6 13
5-6 14
9x(11+12)+
10x(11+13)
0.77
0.0
39.3
19.8
776.7
0.80
96.9
19.3
1,867.0
0.84
23.2
186.9
18.8
3,941.1
0.88
46.2
233.9
18.2
5,108.8
0.92
79.6
373.9
17.7
8,039.4
0.98
102.2
435.8
17.2
9,259.8
1.00
106.1
446.7
16.7
7.0
12,368.6
58.8
259.4
16.2
3.3
17.6
9,908.6
62.4
235.3
15.7
13.8
28.2
12,168.8
38.3
171.0
15.2
24.4
38.8
10,741.5
43.3
14.6
35.0
49.4
3,123.8
Total
77,301.1
From interpolation